Loss of Setd4 delays radiation-induced thymic lymphoma in mice

SETD4 inhibits prostate cancer development by promoting H3K27me3-mediated NUPR1 transcriptional repression and cell cycle arrest

The suppressor of variegation enhancer of zeste-trithorax (SET) domain methyltransferases have been reported to function as key regulators in multiple tumor types by catalyzing histone lysine methylation. Nevertheless, our understanding on the role of these lysine methyltransferases, including SETD4, in prostate cancer (PCa) remains limited. Hence, the specific role of SETD4 in PCa was investigated in this study. The expression of SETD4 in PCa cells and tissue samples was downregulated in PCa cells and tissue specimens, and decreased SETD4 expression led to inferior clinicopathological characteristics in patients with PCa. knockdown of SETD4 facilitated the proliferation of PCa cells and accelerated cell cycle progression. Mechanistically, SETD4 repressed NUPR1 transcription by methylating H3K27 to generate H3K27me3, subsequently inactivated Akt pathway and impeded the tumorigenesis of PCa. Our results highlight that SETD4 prevents the development of PCa by catalyzing the methylation of H3K27 and suppressing NUPR1 transcription, subsequently inactivating the Akt signaling pathway. The findings suggest the potential application of SETD4 in PCa prognosis and therapeutics.

Unmasking the mammalian SET domain-containing protein 4

SET domain-containing protein 4 (SETD4) is a member of a unique class of protein lysine methyltransferases. Here, we introduce the basic features of SETD4 and summarize the key findings from recent studies with emphases on its roles in tissue development and tumorigenesis, and its methylation substrates. SETD4 is expressed in stem/progenitor cells. Ablation of Setd4⁺ cells impedes the repopulation of acinar cells after pancreatic injury. Setd4 deletion in mice promotes the recovery of radiation-induced bone marrow (BM) failure by boosting the function of BM niche, facilitates the generation of endothelial cells and neovascularization of capillary vessels in the heart, enhances the proliferation of BM mesenchymal stem cells and disrupts the TLR4 signaling in BM-derived macrophages. SETD4 expression is also associated with the maintenance of quiescent breast cancer stem cells. While mouse Setd4 knockout delays radiation-induced T-lymphoma formation, elevated SETD4 expression has been observed in some proliferative cancer cells and is associated with a pro-survival potential. Oncogenic fusions of SETD4 have also been identified in cancer, albeit rare. In addition, SETD4 methylates lysine-570 in the C-terminal globular domain of KU70, which enables KU70 translocation to cytoplasm to suppress apoptosis.

SETD4-mediated KU70 methylation suppresses apoptosis

The mammalian KU70 is a pleiotropic protein functioning in DNA repair and cytoplasmic suppression of apoptosis. We report a regulatory mechanism by which KU70’s cytoplasmic function is enabled due to a methylation at K570 of KU70 by SET-domain-containing protein 4 (SETD4). While SETD4 silencing reduces the level of methylated KU70, over-expression of SETD4 enhances methylation of KU70. Mutations of Y272 and Y284 of SETD4 abrogate methylation of KU70. Although SETD4 is predominantly a nuclear protein, the methylated KU70 is enriched in the cytoplasm. SETD4 knockdown enhances staurosporine (STS)-induced apoptosis and cell killing. Over-expression of the wild-type (WT) SETD4, but not the SETD4-Y272/Y284F mutant, suppresses STS-induced apoptosis. The KU70-K570R (mouse Ku70-K568R) mutation dampens the anti-apoptosis activity of KU70. Our study identifies KU70 as a non-histone substrate of SETD4, discovers a post-translational modification of KU70, and uncovers a role for SETD4 and KU70-K570 methylation in the suppression of apoptosis.

Wang et al. identify the methylation of mammalian KU70 by SETD4. This post-translational modification is critical for KU70 localization to the cytoplasm and subsequent suppression of apoptosis.

Recombinant cell-detecting RaDR-GFP in mice reveals an association between genomic instability and radiation-induced-thymic lymphoma

In this study, we aimed to investigate how homologous recombinant (HR)-related genomic instability is involved in ionizing radiation (IR)-induced thymic lymphoma in mice. We divided five-week-old Rosa26 Direct Repeat-GFP (RaDR-GFP) transgenic mice into non-IR control and IR groups and exposed the mice in the IR group to a 7.2 Gy dose of γ-rays, delivered in 1.8 Gy fractions, once a week for four weeks. We then estimated mouse survival and recorded their body, thymus, and spleen weights. The frequency of HR events in the chromosomes of the thymus, bone marrow, and spleen cells and the phenotype of thymic lymphoma cells were analyzed using fluorescence-activated cell sorting (FACS). We found that most mice in the IR group developed thymic lymphoma, their survival rate decreasing to 20% after 180 days of IR exposure, whereas no mice died in the non-IR control group until day 400. The thymus and spleen weighed significantly more in the IR-4-month group than that in the non-IR group; however, we observed no significant differences between the body weights of the control and IR mice. FACS analysis indicated that the frequency of HR events significantly increased at two and four months after the last IR dose in the bone marrow and thymus cells, but not in the spleen cells of RaDR-GFP transgenic mice, suggesting that recombinant cells accumulated in the thymus upon IR exposure. This suggests that IR induces genome instability, revealed as increased HR, that drives the development of thymic lymphoma. Additionally, phenotypic analysis of lymphoma cells showed an increase in the CD4^-/CD8⁺ (CD8SP) cell population and a decrease in the CD4⁺/CD8^- (CD4SP) cell population in the IR-4-month group compared to that in the non-IR group, indicating that IR induces an aberrant cell phenotype characteristic of lymphoma. In conclusion, we observed a significant increase in HR events and abnormal phenotype in thymic lymphoma cells at two and four months after IR exposure in both the thymus and bone marrow tissues, suggesting that genomic instability is involved in the early stages of thymic lymphomagenesis. Our study indicates that HR-visualizing RaDR-GFP transgenic mice can help explore the links between the molecular mechanisms of genome instability and IR-induced tumorigenesis.

Deletion of Mouse Setd4 Promotes the Recovery of Hematopoietic Failure

PURPOSE

Acquired hematopoietic failure is commonly caused by therapeutic and accidental exposure of the bone marrow (BM) to toxic agents. Efficient recovery from BM failure is dictated not only by the intrinsic sensitivity and proliferation capacity of the hematopoietic stem and progenitor cells but also by the BM environment niche. Identification of genetic factors that improve recovery from hematopoietic failure is essential. Vertebrate SETD4 is a poorly characterized and putatively nonhistone methyltransferase. This study aims to identify the roles of SETD4 in BM recovery.

METHODS AND MATERIALS

An inducible SETD4 knockout mouse model (Setd4^flox/flox;Rosa26-CreERT2⁺) was used. Adult sex-matched littermates were treated with tamoxifen to induce Setd4 deletion or oil as the control. Tamoxifen-treated Setd4^wt/wt;Rosa26-CreERT2⁺ mice were included as another control. Those mice were irradiated to induce hematopoietic syndrome and analyzed to identify the roles and mechanisms of Setd4 in of BM recovery.

RESULTS

Loss of Setd4 in adult mice improved the survival of whole-body irradiation-induced BM failure. This was associated with improved recoveries of long-term and short-term hematopoietic stem cells (HSCs) and early progenitor cells. BM transplantation analyses surprisingly showed that the improved recovery was not due to radiation resistance of the Setd4-deficient HSCs but that Setd4-deficient HSCs were actually more sensitive to radiation. However, the Setd4-deficient mice were better recipients for allogeneic HSC transplantation. Furthermore, there was enhanced splenic erythropoiesis in Setd4-deficient mice.

CONCLUSION

These findings not only revealed a previously unrecognized role of Setd4 as a unique modulator of hematopoiesis but also underscored the critical role of the BM niche in recovery from hematopoietic failure. Our study also implicated Setd4 as a potential target for therapeutic inhibition to improve the conditioning of the BM niche before allogeneic transplantation.